Dissolution method of removing bonding agents



United States Patent DISSOLUTION METHOD OF REMOVING BONDING AGENTS Herbert H. Hyman, Chicago, Ill., assignor to the United States of America as represented by the United States Atomic Energy Commission No Drawing. Application March 21, 1949 Serial No. 82,709

1 Claim. (Cl. 134-41 bond have to be removed. This is also necessary in the case of faulty aluminum coatings in order to prepare the slugs for recanning.

Removal of the aluminum cans may be efiected, for instance, by means of a mixture of nitric acid and mercuric nitrate. This process forms the subject matter of the co-pending application of James H. Peterson, Serial No. 551,269, filed August 26, 1944, now Patent No. 2,- 901,343, issued August 25, 1959. The same results may also be accomplished by dissolving the aluminum in a mixture of sodium nitrate-sodium hydroxide solutions; this,

process is described and claimed in the co-pending application of J. Flox, Serial No. 93,185, filed May 13, 1949, now Patent No. 2,893,863, issued July 7, 1959.

'If the aluminum coating was bonded to the uranium by means of an aluminum-silicon alloy and the aluminum has been removed by either of the two methods set forth above or by any conventional method, in most cases a film remains on the uranium. This residue, on an average, amounts to about 0.2% of the original metal weight. This film-like residue may in some cases cause trouble during the dissolution of the uranium, by accumulating in the dissolver and clogging the pipe lines. It is therefore advisable to remove these films prior to further treatment of the slugs in the dissolver.

It has been found that a mixture of nitric acid and bydrofluoric acid is especially well suitable for removing such residual films derived from aluminum-silicon bonds. The concentrations of nitric acid and hydrofluoric acid may be varied widely, for instance from 0.3 to 2 N HF and from 1 to 16 N HNO It is preferred to use a mixture in which the hydrofluoric acid is contained as a 0.5 to 1 N HF solution and the nitric acid in a concentration of 1 to N HNO Studies have been made with regard to the function of rate of solution and concentration. Samples of ,5 part of the Weight of the entire scale residue removed from one slug were treated with 10 cc. of HN0 HF 2,933,421 Patented Apr. 19, 1960 mixtures of various concentrations ranging from 2 to 16 N for the nitric acid and from 0.3 to 2 N for the hydrofluoric acid. The time required for complete dissolution was determined. It was found that in all these experiments the operation proceeded with satisfactory speed, there being no residue left in any instance after three hours. However, in most cases, complete dissolution was attained in less than one hour. The highest rate of dissolution was found to occur with a mixture of 0.75 N HF and 7 N HNO which was less than ten minutes.

Also very satisfactory results were obtained with a mixture containing a 10%-by-weight-solution of nitric acid and l%-solution of hydrofluoric acid, which corresponds to a mixture containing 1.67 N HN0 and about 0.5 N HF. The slugs were immersed in this solution at room temperature or a lower temperature for approximately six hours. The container consisted of a 25-12 stainless chromium-nickel steel. In the case of the use of room temperature for the solution, the dissolver was hardly attacked by the nitric acid-hydrofluoric acid mixture, and it was found that after one month less than 0.0004 in. of penetration into the welded, not heat-treated seams had occurred. After the dissolver had been used for about forty-eight hours, there was no evidence of weld-pitting.

The time of immersion is dependent upon the thickness of the residue to be removed.

Instead of the embodiment described above, namely. immersing the slugs for six hours into the bath at room temperature of lower, the immersion into the HF-I-INO, solution may be reduced to one hour; a subsequent immersion of the slugs into a boiling solution of dilute nitric acid, for instance of 10% nitric acid, for three hours is then advantageous.

The method of this invention yields highly satisfactory results, and slugs treated thereby have a perfectly smooth surface so that the conventional step of sand-blasting before recanning may be eliminated.

Llt will be understood that while there have been described herein certain specific embodiments of this invention, it is not intended to have it limited thereto, since the invention is susceptible to various modifications and changes which come within the spirit of this disclosure and the scope of the appended claim.

What is claimed is:

A method of removing residual aluminum-silicon bonding agents from uranium slugs after the removal of aluminum coatings, comprising immersion of said slugs into a mixture of aqueous nitric acid-hydrofluoric acid solutions, said mixture having an initial concentration of about 0.75 N HF and about 7 N HNO at a maximum temperature of room temperature until said uranium slug is free of said aluminum-silicon bonding agent.

References Cited in the file of this patent UNITED STATES PATENTS 528,513 Davis Oct. 30, 1894 590,966 Cornwall 'Oct. 5, 1897 1,975,818 Work Oct. 9, 1934 OTHER REFERENCES Edwards et al.: Aluminum industry, vol. 2, pages 468, 469, McGraw-Hill Book (30., New York 1930). 

